Vertebral body replacement and insertion methods

ABSTRACT

A vertebral body replacement device, dimensioned for implantation between a first and second vertebral bone is described. The vertebral body replacement device includes a superior endcap, an inferior endcap and a central core between the superior and inferior endcaps. The vertebral body replacement device further includes a fusion aperture extending through the superior and inferior endcaps and central core. The vertebral body replacement device is made of radiolucent material and can be implanted from a lateral or anterior approach to the spine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Application No. 61/454,571, which was filed on Mar. 20,2011. The contents of U.S. Application No. 61/454,571 are incorporatedby reference as part of this application.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to spinal implants, implant insertionassemblies, and surgical methods for replacing at least a portion of oneor more vertebral bodies of the spine.

II. Discussion of the Prior Art

The spine is formed of a column of vertebra that extends between thecranium and pelvis. The three major sections of the spine are known asthe cervical, thoracic and lumbar regions. There are 7 cervicalvertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae, with each ofthe 24 vertebrae being separated from each other by an intervertebraldisc. A series of about 9 fused vertebrae extend from the lumbar regionof the spine and make up the pelvic region of the vertebral column.These fused vertebrae consist of the sacral and coccygeal region of thevertebral column.

The main functions of the spine are to provide support and protect thespinal cord. Even slight disruptions to either the intervertebral discsor vertebrae can result in serious discomfort due to decompression ofnerve fibers either within the spinal cord or extending from the spinalcord. If a disruption to the spine becomes severe enough, damage to anerve or part of the spinal cord may occur and can result in partial tototal loss of bodily functions (e.g. walking, talking, and breathing).Therefore, it is of great interest and concern to be able to bothcorrect and prevent ailments of the spine.

Trauma to the spine (e.g. car accident, sports injury) can causefracturing of one or more of the vertebrae. Certain diseases affectingthe spine (e.g. tumors, osteoporosis) can cause degeneration of thespine. Both trauma and degeneration may result in severe disruption tothe spine. In these circumstances, the complete removal of one or morevertebrae may be required. If one or more vertebrae are removed, areplacement support system must be implanted in order to protect thespinal cord and maintain, or improve, the structure and integrity of thespine.

SUMMARY

According to one broad aspect, a stackable vertebral body replacement isprovided comprising variable size upper and lower endcaps and at leastone center core, all manufactured from a biocompatible material. Forexample, the biocompatible material may include, but is not limited to,poly ether ether ketone (PEEK). The upper and lower endcaps comprise abase and a variable height riser connector. The implant endcap has acavity through the center of the piece to allow for bone fusion. Theendcaps connect to the center core by a mating section on one end of theendcap. The mating section allows the endcaps to be joined to oppositeends of the core, and once locked in place they form a completeassembly. The mating section is designed so the vertebral bodyreplacement can be built inside the body or prior to insertion. Theendcaps are available in heights ranging from 7 mm to 25 mm and anglesranging from zero to eight degrees, allowing for ideal heightreconstruction and restoring lordotic or kyphotic curvature. The centercore comprises a body with a hollow center defining a fusion aperturetherethrough. Both the top and bottom of this center core comprisemating sections which allow the center core to attach to the endcaps andlock into place. The height of the center core ranges from 10 mm to 80mm. During lateral insertion, the center core is inserted between thetwo endcaps using the lateral insertion assembly. If an anteriorinsertion method is used, either a one-piece vertebral body replacement(endcaps and core body as one complete piece) is inserted or the implantis assembled outside the patient and then inserted as a completevertebral body replacement.

In one embodiment, the vertebral body replacement is radiolucent. Theuse of radiolucent material is ideal for use in tumor patients since thesurgeon can see through the implant on an x-ray and monitor the sitepost-surgery. According to this embodiment, radiopaque markers areplaced in the endcaps and the core for use in positioning and alignmentof the vertebral body replacement during insertion. By way of exampleonly, the radiopaque markers may be titanium or tantalum pins.

The lateral inserter assembly is constructed from a biocompatiblematerial, such as stainless steel. It is comprised of a core insertiontool between two slide retainers held apart by an adjustable clamp. Thelateral inserter assembly is used to properly position the endcaps inthe body and guide the core between them inside the body. The centercore of the vertebral body replacement is attached and removed from thecore insertion tool by means of a quick-release on the top of the tool.The two endcaps are attached to the lateral inserter assembly byscrewing them onto endcap retaining rods which slide into holes on eachside of the slide retainer. The center core is placed between the twoslide retainers using the mating sections on the core as a guide betweenthe two slides. Malleting or sliding of the core between the slidesprovides the distraction of the vertebral bodies without the requirementfor an additional device. Once in place, the core insertion tool isdetached from the center core using the quick-release and the lateralinserter assembly are unscrewed from the endcaps. This assembly has theadvantage of allowing for a smaller opening for access to the spine,compared to previous approaches, which will reduce patient recoverytime. Additionally, the stackable assembly provides a slightly lowercost option than expandable cages, while still being able to providemany of the benefits of the lateral approach.

The anterior inserter assembly is used to easily insert the vertebralbody replacement into the spinal cavity and release when properlypositioned. For anterior insertion the stackable vertebral bodyreplacement (core and two endcaps) are assembled outside the body priorto insertion. The anterior inserter assembly comprises a quick-releaseto easily affix and detach the vertebral body replacement from theassembly. For the anterior approach, a separate distractor/sizer will berequired.

A distractor/sizer assembly is used to open the space between twoadjacent vertebrae where the vertebral body replacement will beinserted. The tool is unique since it not only distracts the spinalcolumn, but also measures the desired size of the requirement implant.The distractor/sizer tool comprises two pairs of connected crossed armswith handles at one end (connected by a measurement device) and spreaderarms at the other. Opening the space between the handles at one enddecreases the distance between the spreader arms at the other end.Affixed to the outside of the spreader arms by a pivoting mount is anendcap with anti-migration elements on the outside face to allowsufficient friction to hold onto the surface of remaining vertebraeduring distraction. The vertical distance between the endcaps of thespreader arms can be read from the measurement arm near the handle ofthe device. The distractor/sizer can accommodate heights from 18 mm to120 mm.

The lateral method for inserting the stackable vertebral bodyreplacement is as follows: (1) the patient is placed in the lateraldecubitus position on the operating table and sedated under generalanesthesia, (2) The surgeon ensures proper positioning of the vertebraeto be treated using a fluoroscope, (3) The surgeon makes a smallincision in the skin in the patient's side, over the midsection of thedisc for a single-level fusion or over the intervening vertebral bodyfor a multi-level fusion, (4) Surgical dissection is performed via theplacement of serial dilators, each of which actively providesdirectional nerve localizing electromyographic (EMG) data to the surgeonfor safe navigation near the lumbar nerve plexus. Active neuromonitoringin addition to the use of real-time fluoroscopic guidance insures safetyand accuracy as the expandable tubular retractor is carefully advancedthrough the psoas muscle (for lumbar spine surgeries) to the desireddisc space or vertebral body, (5) The endcaps are inserted coupled tothe lateral insertion tool, (6) The endcaps are placed into positioninside the patient; adjacent the endplates of the vertebral bodies, (7)The clamp holding the two slide retainers is adjusted to the desiredwidth for core insertion, (8) A core is inserted between the two slidesand is guided into place between the endcaps, (9) Malleting the coreinserter assembly down the slides with the core distraction blockattached provides the distraction of the spine. (10) The core is sliddown until it locks into place between endcaps, (11) The core isreleased from the core insertion tool, (12) The insertion tools areremoved and the incision is closed.

The anterior method for inserting the stackable vertebral bodyreplacement body may be performed as follows: (1) The vertebral body tobe replaced is accessed via any anterior approach appropriate for thespinal level, (2) A distractor/sizer is used to distract the endplatesof the adjacent vertebral bodies, and to determine the height of thevertebral body replacement (VBR), (3) The vertebral body replacement isbuilt outside the body based on measurements determined from thedistractor/sizer and attached to the anterior insertion tool and thedistractor/sizer is removed. (4) The insertion tool is detached from thevertebral body replacement and the anterior insertion tool is removed.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is the perspective view of a stackable vertebral body replacementaccording to an exemplary embodiment;

FIG. 2 is the top view of a stackable vertebral body replacement of FIG.1;

FIG. 3 is an exploded perspective view of the vertebral body replacementof FIG. 1;

FIG. 4 is a perspective view of the center core section of the vertebralbody replacement of FIG. 1;

FIG. 5 is the top/bottom view of the core section of the vertebral bodyreplacement implant of FIG. 4;

FIG. 6 is the side (left/right) view of the core section of thevertebral body replacement implant of FIG. 4;

FIG. 7 is the front/back view of the core section of the vertebral bodyreplacement implant of FIG. 4;

FIG. 8 is the perspective view of an endcap of the vertebral bodyreplacement implant of FIG. 1;

FIG. 9 is the front view of an endcap of the vertebral body replacementimplant of FIG. 8;

FIG. 10 is the side (left/right) view of the endcap of the vertebralbody replacement implant of FIG. 8;

FIG. 11 is the back view of the endcap of the vertebral body replacementimplant of FIG. 8;

FIG. 12 is the top/bottom view of the endcap of the vertebral bodyreplacement implant of FIG. 8;

FIG. 13 is the cross-sectional view of the endcap of the vertebral bodyreplacement implant of FIG. 8;

FIG. 14 is the perspective view of the lateral inserter assembly;

FIG. 15 is the bottom view of the lateral inserter assembly of FIG. 14;

FIG. 16 is the top view of the lateral inserter assembly of FIG. 14;

FIG. 17 is the exploded view of the lateral inserter assembly of FIG.14;

FIG. 18 is a perspective view of the bracket assembly of the lateralinserter assembly of FIG. 14;

FIG. 19 is an exploded view of the bracket assembly of the lateralinserter assembly of FIG. 14;

FIG. 20 is a perspective view of the clamp for the lateral inserterassembly of FIG. 14;

FIG. 21 is an exploded view of the clamp for the lateral inserterassembly of FIG. 14;

FIG. 22 is a perspective view of the core inserter assembly;

FIG. 23 is exploded view of the core inserter assembly of FIG. 22;

FIG. 24 is exploded view of top of core inserter assembly of FIG. 22;

FIG. 25 is exploded view of bottom of core inserter assembly of FIG. 22;

FIG. 26 is perspective view of distractor block of FIG. 22;

FIG. 27 is a perspective view of anterior inserter assembly;

FIG. 28 is side view of anterior inserter assembly of FIG. 27;

FIG. 29 is detailed view of bottom end of anterior inserter assembly ofFIG. 27;

FIG. 30 is an exploded view of the bottom end of the anterior inserterassembly of FIG. 27;

FIG. 31 is further exploded view of the bottom end of the anteriorinserter assembly of FIG. 27;

FIG. 32 is an exploded view of the top end of the anterior inserterassembly of FIG. 27;

FIG. 33 is a perspective view on the distractor/sizer assembly;

FIG. 34 is an exploded view of the distractor/sizer assembly of FIG. 33;

FIG. 35 is a bottom view of the distractor/sizer assembly of FIG. 33;

FIG. 36 is an exploded view of the bottom of the distractor/sizerassembly of FIG. 33;

FIG. 37 is a detailed view of the bottom of the distractor/sizerassembly of FIG. 33;

FIG. 38 illustrates the steps involved in using the lateral inserterassembly;

FIG. 39 illustrates the steps involved in using the anterior inserterassembly;

DETAILED DESCRIPTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The stackable vertebral body replacement, anterior andlateral inserter assemblies, distractor/sizer and methods forimplantation disclosed herein boasts a variety of inventive features andcomponents that warrant patent protection, both individually and incombination.

FIGS. 1-13 illustrate an exemplary embodiment of a stackable vertebralbody replacement 10 according to one embodiment of the presentinvention. The stackable vertebral body replacement 10 includes a centercore section 11 and two endcaps 12. The core section 11 and the twoendcaps 12 are made from a biocompatible material. For example, thecomponents may be machined from implantation-grade polyether etherketone (PEEK). In one embodiment, six sides comprise the center core 11.The following sides of the core are opposite each other and areidentical: top 34 and bottom 35, front 36 and back 37, and left 38 andright 39. The top 34 and bottom 35 sides of the core sections 11 havemating sections 13, which allow the core 11 to couple to the matingsections 14 of the endcaps 12. The core 11 is may vary in height from 10mm to 80 mm. The core 11 is held in place between the two endcaps 12 bythe stops 15 on front 36 and back 37 of the core 11 which lock into thelocking assembly 16 on the back of the endcap 12. A guide 33, helpsposition the core 11 into the mating sections 14 on the endcaps 12during insertion. Additionally, a protrusion 17 on the mating section 13increases the friction between the core 11 and endcaps 12 holding theassembly together. The top of the core 11 has holes 18 extendinglongitudinally therethrough, in which radiopaque markers are placed toverify alignment during insertion. On top of the core 11 there areadditional holes 19 which allow entry of the core insertion assemblypins 77 for lateral insertion. The side of the core 11 has holes 20 forattachment to the anterior inserter assembly 90 for anterior insertion.Additional holes 21 in the side of the core 11 allow for insertion ofadditional radiopaque markers for verifying alignment during insertion.

The endcaps 12 comprise a variable length base 22 and a variable heightriser 23. In one embodiment, the endcap base 22 is rectangular withfront 133, back 134, left 135, right 136, top 137, and bottom 138 sides.The endcaps 12 range in height from 7 mm to 25 mm. The endcap 12 iscomprised of a cavity 24 through the piece which runs from the front 133to the back 134 to allow for bone fusion through the vertebral bodyreplacement. In one embodiment, in addition to the cavity 24, the endcapbase 22 has additional holes 25 which are cut through the base materialat opposite ends of the base, also to promote bone fusion with theendcap 12. On the top 137 and bottom 138 of the endcaps 12 are screwholes 26 to allow for connection to the endplate retaining rods 45 ofthe lateral inserter system 40. Additionally on top 137 and bottom 138of the endcaps 12 are holes 27 for radiopaque markers for properalignment during insertion and a hole 32 to promote bone fusion. Theside of the implant has an additional hole 28 for a radiopaque markerand holes 29 to promote fusion. The front 133 of the endcap 12 hasanti-migration elements 30 designed to grip the ends of the vertebraeafter implantation in order to maintain its proper spinal alignment.Additionally, there are a plurality of small holes 31 in the front 133of the endcap 22, partially through the base for the insertion ofradiopaque markers which guide insertion and maintain implant position.

FIGS. 14-26 illustrate the lateral inserter system 40 according to oneembodiment of the present invention. This embodiment of the lateralinserter system is comprised of two slide retainers 41, a core inserter42, two bracket assemblies 43, and a clamp assembly 44.

The slide retainers 41 are constructed of a biocompatible material, suchas stainless steel and are positioned on either side of the coreinserter 42. Endcap retaining rods 45 are slid into the in the top ofthe slide retainer 41 and travel the complete length of the slideretainer 41. On the top of the endcap retaining rod 45 is a knurled knob46 and the opposite end is a threaded end tip 47. The threaded end tip47 can be attached to the top of the endcap 12 in screw hole 26. Thefront of the slide retainer 41 has a handgrip 48 to assist the surgeonin handling the device. Below the handgrip 48, on the front of the slideretainer 41 is a vertical height adjustment section 49. This verticalheight adjustment section 49 allows varying height adjustment of thebracket assembly 43. On the inside of the slide retainer 41 is a matingsection 50 which allows for coupling the core 11 onto the inside of theslide retainer 41 between the two endcaps 12.

The bracket assemblies 43 maintain position of the lateral insertersystem 40 in the body during surgery. The vertical position of thebracket assembly 43 along the slide retainer 41 is adjustable in oneembodiment by manually retracting the slide locks 51 by pulling theknobs 52 outward on the bracket assembly 43. The bracket assembly 43 ispositioned vertically along the slide retainer 41 as required and theknobs 52 are released when in the desired position. In one embodiment,the slide locks 51 are held extended in the locked position by theextension force of a spring 53 inside the bracket assembly 43. Here, theslide lock 51 is affixed to the knob 52 by a pin 54 inserted through ahole 55 in the knob and a hole 56 in the top of the slide lock 51. Theinside edges 57 of the bracket assembly 43 are curved to allow thebracket assembly 43 to move along the outside edges of the slideretainer 41.

The clamp assembly 44 allows for both measuring the space betweenvertebral bodies in the spine and maintaining the proper space betweenthe slide retainers 41 during lateral insertion. The clamp assembly 44is made of a biocompatible material, such as stainless steel. The upperarm 58 of the clamp assembly 44 is affixed to the slide retainer 41 bymeans such as a screw 59 and a retaining nut 60. The lower arm 61 of theclamp assembly is attached to the opposite slide retainer 41 in similarfashion. The measurement bar 62 is mounted into the end of the upper arm58 opposite the slide retainer 41 attachment point. The lower arm 61travels along the measurement bar 62 with the opposite end affixed tothe slide retainer mount 41. The lower arm 61 is held in place by alocking device 68 which is attached to the lower arm 41 by the mountingpin 65. A handle 63 is attached to a locking screw 64 inside the lowerarm. Turning the handle 63 engages and disengages the locking device 68,restricting and allowing travel of the lower arm 41 along themeasurement bar 62 which changes the distance between the slideretainers 41.

The core inserter 42 is made of biocompatible material, such asstainless steel. In one embodiment, the core inserter 42 comprises anouter container 66, an inner rod 67, a core distractor block 80, a quickrelease 69 and a locking nut 70. The inner rod 67 slides within thehollow outer container 66 and is attached at the upper end by releasepins 71 which travel through holes in the inner rod and into slots 72 inthe outer container which limit the travel of the rod. The quick-release69 fits around and is attached to the outer container 66 by two lockpins 73. The inside of the locking nut 70 is threaded and fits aroundthe outer container 66 and screws onto the threaded area 74 on theoutside of the container. A spring 75 fits around the outer container 66between the quick-release 69 and the locking nut 70. The spring 75 iscompressed and the force on the spring is translated as a downward forceon the inner rod 67, keeping the arms 77 at the end of the core inserter42 extended unless upward force is applied to the quick-release 69counteracting spring 75 force. The lower end of the inner rod 67 isattached to the center pin 76 holding the core inserter arms 77together. Two pivot pins 78 allow the core inserter arms 77 to pivotaround the center pin 76, opening and closing the arms.

With the core inserter arms 77 together, the outer container 66 slidesinto the distractor block 80. The distractor block 80 is made ofbiocompatible material. For example, the components may be machined fromimplantation-grade polyether ether ketone (PEEK). The distractor block80 is held onto the core inserter 42, in one case, by two ball detents78 on both sides of the core inserter 42. The top 139 and bottom sides139 of the distractor block 80 have a mating section with connectors 81which are smaller than those of the center core 11 in order to take thedownward load off the core 11 during distraction. The center of thedistractor block 80 is hollow to allow the bottom of the outer container66 to slide into and attach to the distractor block 80. On the inside ofthe left 143 and right 144 sides of the distractor block 80 are recessedholes 83 where the ball detents 79 from the outer container 66 meet withand attach the distractor block 80 to the outer container 66. Pullingthe distractor block 80 vertically down off the outer container 66 willrelease the ball detents 79, allowing the distractor block 80 to beremoved from the outer container 66.

FIGS. 27-32 illustrate the anterior inserter system 90 according to oneembodiment of the present invention. The anterior inserter system 90 iscomprised of a hollow outer container 91 a collet 92, a lock 93, abracket assembly 94, an inner shaft 95 and two bracket arms 96 whichattach to the center core 11. The anterior inserter system 90 isconstructed from biocompatible material, such as stainless steel. Theend of the bracket arms 96 are machined to enable them to affix to thecore 11 by traveling through holes 20 on the core 11 and grasping theinside edge of the core material. Both bracket arms 96 are connected tothe end of the inner shaft 95 by means such as a center pin 97. Thebracket arms 96 are also connected to the bracket 94 by two pivot pins98. The bracket assembly 94 allows vertical movement of the inner shaft95, which pivots the bracket arms 96 around the pivot pins 98 causingthe bracket arms 96 to open and close. The pivot pins travel throughholes 99 on the bracket 94 which affix the bracket arms 96 to thebracket assembly 94.

At the opposite end of the anterior inserter system 90 from the bracketassembly 94 is the release assembly. The release assembly is comprisedof the collet 92, a lock 93 a spring 100 and two release pins 101. Therelease pins 101 go through the top of the inner shaft 95 and throughslots 102 in the outer container 91. The release pins 101 ride in theslots 102 allowing for some limited, vertical movement of the innershaft 95 within the outer container 91. A spring 100 is placed on theinside of the outer container 91 at the end, between the end of theouter container 90 and the end of the inner shaft 95 allowing fortension being placed upon the inner shaft 95. The force of the spring100 causes downward force on the inner shaft 95 which causes the bracketarms 96 to pivot around the pivot pins 98 and the bracket arms 96 tospread out. The spread bracket arms 96 of the anterior inserter 90 affixthe center core 11 to the anterior inserter 90. Upward force on thecollet 92, causes the inner shaft 95 to move upwards, causing thebracket arms 96 to move toward the center (retract), allowing theanterior inserter system 90 to be removed from the center core 11 afterbeing property positioned in the body. The outer container 91 is travelsthrough the hole in the center of the collet 92 and the collet 92 isaffixed to the outer container 91 by the release pins 101 which travelthrough the collet 92, the outer container 91 and inner shaft 95.Located just above the collet 92 on the outer container is a threadedarea 103. The inside of the lock 93 is threaded. The top of the outercontainer 91 is placed through the center of the lock 93. The lock 93 isthen screwed onto the outer container 91 onto the threaded area 103until it meets the edge of the collet 92. The lock 93 is used tomaintain the collet 92 in the desired position during insertion of thevertebral body replacement. Adjusting the position of the lock 93 on thethreaded area 103 allows for movement in the collet 92 on the outercontainer 91.

FIGS. 33-37 illustrate the distractor/sizer 110 according to oneembodiment of the present invention. The distractor/sizer 110 isconstructed from a biocompatible material such as stainless steel and iscomprised of lower arms 111 held together in the center of the arm bythe lower center screw 112. The top of the lower arms 111 are affixed tothe bottom of the upper arms 113 by two screws 114. The upper arms 113pivot around the upper center screw 115. The outer edges of the upperarms 113 are curved to form a handgrip 116. A pair of flexible bars 117are affixed between the upper arms 113 by mounting pins 118. Theflexible bars 117 hold the upper arms 113 apart and provide someresistance as the upper arms 113 are closed together. As the upper arms113 are moved together (closed), the bottom end of the upper arms 113move apart. This movement causes the upper end of the lower arms 111 tomove apart and the bottom of the lower arms 111 with the endplates 119to move apart, causing distraction. A measurement bar 120 is affixed toone end of the upper arms 113 by a mounting pin 121. The other end ofthe measurement bar 120 travels through a hole 122 on the other upperarm 113. A collar 123 is attached to the end of the measurement bar 120by an endcap 124 affixed to the end of the measurement bar 120. Theendplates 125 are affixed by threaded screws 126 and caps 127 to endcapbrackets 128 which have an attaching point 129 which affix the endcapbrackets 128 to the bottom end of the lower arms 111 via a pivot pin130. The outside edges of the endplates 125 have anti-migration elements131 to maintain the proper position of the distractor/sizer 110 on thevertebral bodies during distraction. The measurement bar 120 iscalibrated to allow the surgeon to determine the size of vertebral bodyreplacement required for the patient. The distractor/sizer 110 allowsfor distraction and sizing to be completed with one surgical tool.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined herein.

What is claimed is:
 1. A vertebral body replacement device dimensionedfor implantation between a first and second vertebral bone, comprising:a superior endcap comprising a first bone contacting base, having afirst front surface configured to contact a bone and an opposing firstback surface, and a first body portion, which extends from said firstbone contacting base back surface and ends in a first body portionmating surface, said first body portion mating surface including a firstmating feature which is opposite said first bone contacting base frontsurface, said mating surface including a first keyed recess lockingassembly, and said superior endcap including a fusion aperture extendingthrough the first bone contacting base and the first body portion; aninferior endcap comprising a second bone contacting base and a secondbody portion, said second body portion including a second matingsurface, including a second mating feature and a second keyed recesslocking assembly, opposite said second bone contacting base, and saidinferior endcap including a fusion aperture extending through the secondbone contacting base and the second body portion; and a rigid centralcore having an axial cross-section that is similar in shape to an axialcross-section of at least one of the superior and inferior endcaps, andhaving a superior mating surface having a superior mating featurecorresponding to said first mating feature of the superior endcap and aninferior mating surface having an inferior mating feature correspondingto said second mating feature of the inferior endcap, said central corefurther including a fusion aperture extending therethrough; wherein saidmating surfaces of the central core each comprise a guide protrusion ona posterior end and a keyed tab stop assembly complementary to saidkeyed recess locking assemblies on an anterior end, and wherein saidguide protrusions are sized and configured to slidably guide the coreinto engagement with the endcaps, and wherein said keyed tab stopassemblies engage the keyed recess locking assemblies when the core isfully seated to prevent overinsertion of the central core, wherein saidcentral core has a maximum width that is less than the width of at leastone of the superior endcap and the inferior endcap.
 2. The vertebralbody replacement device of claim 1, wherein the superior endcap,inferior endcap and central core are constructed of the same material.3. The vertebral body replacement device of claim 2, wherein thematerial is PEEK.
 4. The vertebral body replacement device of claim 1,the central core has a height greater than 10 mm.
 5. The vertebral bodyreplacement device of claim 4, wherein the central core has a heightless than 80 mm.
 6. The vertebral body replacement device of claim 1,wherein at least one of the superior endcap and the inferior endcapincludes a radiopaque marker.
 7. The vertebral body replacement deviceof claim 6, wherein the core includes a radiopaque marker.
 8. Thevertebral body replacement device of claim 1, wherein the superiorendcap and inferior endcap have a height greater than 7 mm.
 9. Thevertebral body replacement device of claim 8, wherein the superiorendcap and inferior endcap have a height less than 25 mm.
 10. Thevertebral body replacement device of claim 1, wherein the first bonecontacting base of the superior endcap includes anti-migration features.11. The vertebral body replacement device of claim 10, wherein thesecond bone contacting base of the inferior endcap includesanti-migration features.
 12. The vertebral body replacement device ofclaim 1, wherein the axial cross-section of the core is generallyrectangular.